The Wasatch Fault is an

active fault An active fault is a fault that is likely to become the source of another earthquake sometime in the future. Geologists commonly consider faults to be active if there has been movement observed or evidence of seismic activity during the last 10,0 ...

located primarily on the western edge of the

Wasatch Mountains The Wasatch Range ( ) or Wasatch Mountains is a mountain range in the western United States that runs about from the Utah-Idaho border south to central Utah. It is the western edge of the greater Rocky Mountains, and the eastern edge of the G ...

in the U.S. states of

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...

and

Idaho Idaho ( ) is a U.S. state, state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Monta ...

. The fault is about long, stretching from southern Idaho, through northern Utah, before terminating in central Utah near the town of Fayette. The fault is made up of ten segments, five of which are considered active. On average the segments are approximately long, each of which can independently produce earthquakes as powerful as local magnitude 7.5. The five active segments from north to south are called the

Brigham City Brigham City is a city in Box Elder County, Utah, United States. The population was 17,899 at the 2010 census. It is the county seat of Box Elder County. It lies on the western slope of the Wellsville Mountains, a branch of the Wasatch Range ...

Fault Segment, the

Weber Weber (, or ; German: ) is a surname of German origin, derived from the noun meaning " weaver". In some cases, following migration to English-speaking countries, it has been anglicised to the English surname 'Webber' or even 'Weaver'. Notable pe ...

Fault Segment, the

Salt Lake City Salt Lake City (often shortened to Salt Lake and abbreviated as SLC) is the capital and most populous city of Utah, United States. It is the seat of Salt Lake County, the most populous county in Utah. With a population of 200,133 in 2020, th ...

Fault Segment, the Provo Fault Segment and the Nephi Fault Segment. The Wasatch Fault is a normal (vertical motion) fault which forms the eastern boundary of the Basin and Range geologic province which comprises the geographic

Great Basin The Great Basin is the largest area of contiguous endorheic watersheds, those with no outlets, in North America. It spans nearly all of Nevada, much of Utah, and portions of California, Idaho, Oregon, Wyoming, and Baja California. It is noted fo ...

. The Wasatch Mountains have been uplifted and tilted to the east by movement of the fault. The average vertical displacement rate of the fault over its history is approximately 0.8–1.2 mm/yr.

Geological history

During the past 10,000 years, major earthquakes (magnitude 7.0 or greater) occur about every 900–1,300 years along any one of the five central segments of the Wasatch Fault. However, the average time-span between earthquakes along the entirety of the central segments is about 300 years. The segment that underlies

produced a major earthquake approximately 1,200–1,300 years ago, the

, Provo, and Nephi segments each produced one about 200–700 years ago and the

fault segment has not produced a major earthquake in about 2,200–2,800 years.

Earthquake assessment

Statistically, the Wasatch Fault is overdue for another major earthquake. Experts have given a 57% probability of an earthquake magnitude 6.0 or greater occurring within the next 50 years. However, statistical frequency does not necessarily imply periodic behavior, though it can serve as a good indicator.

Liquefaction In materials science, liquefaction is a process that generates a liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics. It occurs both naturally and artificially. As an example of th ...

due to a strong earthquake is of particular concern because many highly populated areas along the

Wasatch Front The Wasatch Front is a metropolitan region in the north-central part of the U.S. state of Utah. It consists of a chain of contiguous cities and towns stretched along the Wasatch Range from approximately Provo in the south to Logan in the nort ...

lie on soft lake sediments, remnants of

Lake Bonneville Lake Bonneville was the largest Late Pleistocene paleolake in the Great Basin of western North America. It was a pluvial lake that formed in response to an increase in precipitation and a decrease in evaporation as a result of cooler temperature ...

. A strong earthquake on the Wasatch Fault could trigger landslides, cause mass liquefaction, and flooding of low-lying areas forming near lakes due to

subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope mov ...

and tilting. The quake may also rupture the surface causing displacement of up to , and severely damage gas, electric, water, communication, and transportation lifelines. A report released by Bob Carey of Utah's Office of Emergency Services and published by the ''

Deseret News The ''Deseret News'' () is the oldest continuously operating publication in the American west. Its multi-platform products feature journalism and commentary across the fields of politics, culture, family life, faith, sports, and entertainment. Th ...

'' in April 2006 predicts that a strong earthquake occurring in Salt Lake City could kill up to 6,200 people, injure 90,000, and cause US$40 billion in economic losses. Due to the earthquake danger not being well known when many structures were built in the area, at least 42% of the buildings along the Wasatch Front are at risk of moderate to severe damage in the event of a strong earthquake. Many buildings, such as hospitals and schools, are located directly atop the Wasatch Fault. Approximately 50% of hospital beds in Salt Lake City are at risk. Currently, about 80% of Utah's population live along the Wasatch Fault, representing the largest earthquake threat in the interior Western U.S. On the west end of Salt Lake Valley is another fault zone called the West Valley fault zone that spans 9 miles (16 km) north-northwest. Recent trench studies have shown that the West Valley fault tends to rupture simultaneously with the Wasatch Fault, compounding issues such as liquefaction, landslides and flooding. The two faults likely converge into a single fault deep underneath Salt Lake Valley. On March 18, 2020, a 5.7 magnitude earthquake occurred just north of Magna, causing moderate damage. In March 2021, a new study based on evaluations of the 2020 earthquake and aftershocks determined that the Wasatch Fault undercuts the Salt Lake Valley at a shallower depth than previously thought. This means that a large earthquake on the Salt Lake section of the Wasatch Fault would likely cause more ground shaking and greater damage than previously expected.

Public awareness

As awareness has increased since the 1980s, many key structures in the region have been undergoing extensive

seismic retrofitting Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with our recent exp ...

, reservoirs on the fault have been drained, and development in at-risk areas curtailed
The Utah Earthquake Program
(a partnership between The Utah Geological Survey,

University of Utah The University of Utah (U of U, UofU, or simply The U) is a public research university in Salt Lake City, Utah. It is the flagship institution of the Utah System of Higher Education. The university was established in 1850 as the University of De ...

Seismograph Stations, and Utah Division of Emergency Management) has been actively working to educate communities in Utah, conduct research, and investigate technologies that can mitigate the damage caused by a strong earthquake along the Wasatch Fault. Salt Lake City is currently utilizing federal grant funds to run a ''Fix the Bricks'' program targeting seismic safety upgrades in unreinforced masonry buildings.

References

USGS factsheet

External links

Utah Geological Survey Public Information Series 40: The Wasatch Fault Utah Geological Survey presentation about the fault Utah Geological Survey Quaternary Fault and Fold DatabaseSalt Lake City Emergency Management
{{DEFAULTSORT:Wasatch Fault Geology of Utah Geology of Idaho Seismic faults of the United States Wasatch Front